Method for storing a pellicle

ABSTRACT

There is provided a method for packing a pellicle container in plastic resin bags, which is meant to prevent foreign particles from reaching the pellicle container and eventually the product pellicle; the points of the invention lie in that bags are either antistatic or of special cleanroom-use grade prepared and preserved in a cleanroom environment.

PRIORITY CLAIMED

The present non-provisional application claims priority, as per ParisConvention, from Japanese Patent Application No. 2011-071582 filed onMar. 29, 2011, the disclosure of which is hereby incorporated byreference herein in its entirety.

FIELD OF THE TECHNOLOGY

The present invention relates to a method for storing a pellicle or thelike which is finished in the manufacturing process conducted in a cleanroom.

BACKGROUND OF THE INVENTION

A pellicle for lithography manufactured in a clean room is stored in acontainer tailored for it and then wrapped in a bag made of a syntheticresin. In order to prevent the pellicle container and the pellicle fromtaking electrostatic charge, the bag adopted is commonly of antistatictype.

In the case of an antistatic type bag, an antistatic additive isingrained in the bag material or a metallic film is deposited on the bagsurface so as to provide the bag with electric conductivity; however,these become sources of foreign particle generation, and thus are apt tocontaminate the pellicle container packed in the bag, depending on theseverity of the circumstances wherein the pellicle container istransported or exposed, and furthermore as the container is removed fromthe bag and is opened, the antistatic agent or the like sticking to thelid or other parts of the pellicle container would contaminate thepellicle stored in the container.

SUMMARY OF THE INVENTION Problems the Invention Seeks to Solve

In view of the above circumstances, it is an object of the presentinvention to provide a method for storing a pellicle whereby foreignparticle generation is restricted during the storage, transportation andunpacking, the pellicle stored in the pellicle container or the like isscarcely contaminated.

Means to Solve the Problems

The present invention was contrived to attain this object and thepellicle storing method according to the present invention ischaracteristic in that a container storing a pellicle is placed in afirst bag of cleanroom-use grade, and after closing the first bag thefirst bag is placed in a second bag having an antistatic function, andafter closing the second bag the second bag is placed in a third baghaving an antistatic function and then the third bag is closed.

The bag of cleanroom-use grade can be a bag made in a cleanroom ofcleanliness class 1000 or cleaner, according to Federal Standard 209EAirborne Particulate Cleanliness Classes, and the bags having theantistatic function have a surface resistance of 9.9×10¹¹ ohm/cm² orlower. Also, it is preferred that the bag closing work is conducted in acleanroom of cleanliness class 1 or cleaner.

Effects of the Invention

According to the present invention, a clean bag is used as the innermostfirst bag, and antistatic bags are used as the second and third bagswhereby foreign particles are prevented from sticking to the containerof the product pellicle as well as the product pellicle itself, and alsothe occurrence of electrostatic charge is minimized and thus the productcontamination is prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing to show how a pellicle is stored accordingto the present invention.

EMBODIMENT OF THE INVENTION

The present invention relates to a method for storing a pelliclecontainer packed with a product pellicle, in a cleanroom, and theinvention requires that the pellicle container packed with the pelliclebe enveloped in a three-ply manner, i.e., in a three-bag systemconsisting of, from inner to outer, an innermost clean bag withoutantistatic function, a second innermost antistatic bag, and an outermostantistatic bag, so that the pellicle container is not allowed to be indirect contact with a bag carrying an antistatic additive, and as theresult the pellicle stored in the pellicle container is kept safe fromcontamination and the outer antistatic bags prevent the occurrence ofelectrostatic mishap caused by static charge on the bags.

Now we will explain the present invention in detail using FIG. 1 asreference. In FIG. 1, bags 3, 4, and 5 are seen transparent, but any oneof them can be opaque.

It is seen from FIG. 1 that a pellicle container 2 packed with apellicle 1, of which the frame is hatched, is inside a first bag 3 ofcleanroom-use grade, and the first bag 3 is enclosed in an antistaticsecond bag 4, and the second bag 4 is enclosed in an antistatic thirdbag 5.

The sizes of the bags used in the present invention must be such thateach bag can contain the respectively expected contents thereof. Thethicknesses and qualities of the resin sheets to make the bagspreferably are such that they allow closing of the respective bag bythermal sealing without the bag being over-softened or destroyed by theheat applied to it. If the thickness is too large, it is not easy tomolten the sheet for the sealing so that the preferable thickness may be50-200 micrometers.

The material to make the bag is not limited, but with respect to theinnermost (first) bag which comes in direct contact with the pelliclecontainer, it would be preferable to adopt a resin such as polyethylene,nylon, polypropylene, and polyester, or a composite sheet consisting oflayers of two or more of these materials. The first bag must be such aone as is of cleanroom-use grade, and manufactured in a cleanroom ofcleanliness class 1000 or cleaner, and has been preserved under cleanconditions.

This first bag 3 is contained in the second bag 4. Like the first bag,the second bag may be made of a resin such as polyethylene, nylon,polypropylene, and polyester, or a composite sheet consisting of layersof two or more of these materials, plus a metallic layer deposited onthe resin or an antistatic agent engrained in the resin for the creationof antistatic characteristic. As for the degree of the antistaticcharacteristic to impart to the resin, it is desirable if the bag willhave a surface resistivity of 9.9×10¹¹ ohm/cm² or lower, which is thecase commonly adopted in the antistatic commodities.

The pellicle container packed in the first and the second bags is thenput into the third bag 5. The third bag 5, being disposed to come indirect contact with the external environment, is supposed to be openedimmediately before the content is brought into the cleanroom so as toavoid the entrance of the contamination on the third bag 5 into thecleanroom.

Therefore, depending on the cleanliness of the cleanroom into which thecontent is brought, the number of the bags in which the pelliclecontainer is contained may be increased.

Like the second bag, the third bag may be made of a resin such aspolyethylene, nylon, polypropylene, and polyester, or a composite sheetconsisting of layers of two or more of these materials, plus a metalliclayer deposited on the resin or an antistatic agent engrained in theresin for the creation of antistatic characteristic.

The same applies to a fourth bag, a fifth and so on.

Examples

Now, we will describe examples of the present invention. In thefollowing example, reference examples, and comparative examples, thebags of cleanroom-use grade used were polyethylene bags which had beenmade and cleansed in cleanrooms of cleanliness class 1000 or cleaner,and the antistatic bags used were polyethylene bags which had beenengrained with an antistatic agent to have antistatic function (surfaceresistivity of 9.9×10¹¹ ohm/cm² or lower).

Example 1

First, a pellicle container packed with a pellicle was inserted into afirst bag of cleanroom-use grade having a sheet thickness of 70micrometers until the former reached the bottom of the latter, and theopening of the bag was thermally sealed off. Next, the first bagcontaining the pellicle container was inserted into an antistatic secondbag with a sheet thickness of 70 micrometers, and the opening of thesecond bag was sealed off thermally.

Lastly, the sealed second bag was inserted into an antistatic third bagwith a sheet thickness of 100 micrometers, and the opening of the latterwas thermally sealed off. This was put into a corrugated card-board boxfilled with cushion pieces, and after closing the card-board box, thebox was set on a vibration test equipment and was subjected to avertical vibration of a frequency of 10 Hz at an acceleration rate of 1G for twenty-four hours.

Next, the box was brought into a cleanroom where it was opened and theresearchers observed that white substance, which was thought to be theantistatic agent, had bled out on the surfaces of the second and thethird bags. This substance was also seen to have stuck to the outersurface of the first bag, but the surfaces of the pellicle containerinside the first bag was clean of the substance; this was furtherconfirmed when the container was inspected in a dark room inside thecleanroom, where a 300,000-lux beam lump was used for the inspection forthe foreign matters.

Also, the container was opened and the product pellicle was inspected inthe same manner as stated above, and the surfaces of the product did notshow any sign of sticking substance.

Reference Examples 1 and 2

In Reference Example 1, the first bag and the second bag used were ofcleanroom-use grade having a sheet thickness of 70 micrometers, and thethird bag used was an antistatic bag having a sheet thickness of 100micrometers. In Reference Example 2, the first and the second and thethird bags used were all of cleanroom-use grade having a sheet thicknessof 70 micrometers. Except for these differences, all the particulars ofExample 1 were observed in the Reference Examples; thus the openings ofthe bags were thermally sealed, and after the 24-hour long vibrationtest, the box and bags were opened in the cleanroom and the containerfor the product (pellicle) was taken to the dark room in the cleanroomfor inspection with the 300,000 lux beam lamp and the result was that inboth of the reference examples the amount of foreign substance on theproduct had increased. This result was entered in Table 1 together withthe result from Example 1.

Reference Examples 3 through 5

In Reference Example 3, all the particulars of Example 1 were observedexcept that an antistatic bag of a sheet thickness of 70 micrometers wasused as the first bag; in Reference Examples 4 and 5, all theparticulars of Example 1 were observed except that either or both of thesecond and the third bags were of cleanroom-use grade (ref. Table 1).The corrugated card-board box was brought into the cleanroom where itwas opened and the researchers observed that white substance, which wasthought to be the antistatic agent, had bled out on the surfaces of thefirst and the second and the third bags.

This substance was also seen to have stuck to the outer surface of thepellicle container. This presence of the white powdery substance on thecontainer was further confirmed when the container was inspected in thedark room inside the cleanroom, where the 300,000-lux beam lump was usedfor the inspection for the foreign matter. The container was opened andthe product pellicle was inspected in the above-mentioned manner, andthere was found foreign material sticking to the pellicle and by meansof an infrared microscope spectroscopy the foreign material wasidentified to be of the same make-up as the antistatic agent ingrainedin the first bag. This result is entered in FIG. 1.

Comparative Example 1

This is an example which has been conventionally practiced, wherein onlyone antistatic bag is used: the pellicle container containing a pelliclewas inserted in the antistatic bag of a sheet thickness of 100micrometers; after sealing the opening of this bag thermally, the sameprocedure as in Example 1 was followed including the 24-hour vibrationtest, opening of the box and the bag within the cleanroom, opening ofthe pellicle container and taking the pellicle out therefrom, and theinspection with the 300,000 lux beam lump in the dark room inside thecleanroom. This procedure confirmed that there was an increased amountof foreign substance on the product pellicle. This result was alsoentered in Table 1 together with those of Example and ReferenceExamples.

TABLE 1 Increase in number of foreign charging particles voltage of onfirst bag second bag third bag product product Example 1 cleanroom-useantistatic bag antistatic bag 0 V 0 bag Reference cleanroom-usecleanroom-use antistatic bag 100 V  1 Example 1 bag bag Referencecleanroom-use cleanroom-use cleanroom-use 450 V  10 Example 2 bag bagbag Reference antistatic bag antistatic bag antistatic bag 0 V 5 Example3 Reference antistatic bag cleanroom-use antistatic bag 0 V 1 Example 4bag Reference antistatic bag cleanroom-use cleanroom-use 0 V 2 Example 5bag bag Comparative antistatic bag none none 0 V 3 Example 1

EXPLANATION OF THE REFERENCE NUMERALS

1: pellicle

2: pellicle container

3: first bag (of cleanroom-use grade)

4: second bag (antistatic type bag)

5: third bag (antistatic type bag)

1. A pellicle storing method comprising steps of placing a containercontaining a pellicle in a first bag of cleanroom-use grade, closing anopening of said first bag, placing said first bag in a second bag havingan antistatic function, closing an opening of said second bag, placingsaid second bag in a third bag having an antistatic function, andclosing an opening of said third bag.
 2. A method as claimed in claim 1,wherein said first bag has been manufactured and preserved in acleanroom of cleanliness class 1000 or cleaner.
 3. A method as claimedin claim 1, wherein said bags having an antistatic function have asurface resistance of 9.9×10¹¹ ohm/cm² or lower.
 4. A method as claimedin claim 1, wherein said method including bag closing steps areconducted in a cleanroom of cleanliness class 1 or cleaner.